He is five. I have only owned him 10 months, since September. He didn’t have these lines then, and I didn’t notice them in the winter, only when he shed out.
They don’t seem to be from riding/spurs as they are too high up on his torso. And, they didn’t go away when not ridden for two weeks. (But they are on both sides so it ![ makes me think it must be riding. He doesn’t need any leg though…)
The skin underneath is completely smooth – you can close your eyes, rub your hands over, and not detect any difference in hair or skin.
He has them on both sides. They don’t go away with a bath.
He has a utility broom brush in his stall that he can scratch against, but is seems odd the brush marks would make such uniform line.
He has sensitive skin, but these do not bother him in the least.
Any ideas?